Document management apparatus, document management system, and non-transitory computer readable medium

ABSTRACT

A document management apparatus includes a memory that stores document data in which confidential information is concealed, and a display controller that, in searching the document data according to an input search condition, displays a location where the confidential information is concealed in the document data when the document data stored in the memory and including the confidential data included in the input search condition is displayed as a search result.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2017-135894 filed Jul. 12, 2017.

BACKGROUND (i) Technical Field

The present invention relates to a document management apparatus, a document management system, and a non-transitory computer readable medium.

(ii) Related Art

Techniques of searching a document including secret information or confidential information are available.

Search may be performed on a document including secret information (hereinafter generally referred to as confidential information). One technique contemplated may assign an access right to each target index including characters and location information. In such a case, an operation to determine whether each target index has an access right is performed during the search, leading to an increase in processing costs. A system that searches a vast amount of documents, such as 10 million documents, may be subject to a substantial delay in processing.

To ensure confidentiality, confidential information of a document may be blacked out and then stored. If the document with the confidential information thereof blacked out leaks, making a determination as to whether the original document matches the leaked document is difficult. As a result, traceability is not ensured.

SUMMARY

According to an aspect of the invention, there is provided a document management apparatus. The document management apparatus includes a memory that stores document data in which confidential information is concealed, and a display controller that, in searching the document data according to an input search condition, displays a location where the confidential information is concealed in the document data when the document data stored in the memory and including the confidential data included in the input search condition is displayed as a search result.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiment of the present invention will be described in detail based on the following figures, wherein:

FIG. 1 illustrates a system configuration of a document management system of an exemplary embodiment;

FIG. 2 is a functional block diagram illustrating a log system of the exemplary embodiment;

FIG. 3 is a configuration block diagram illustrating the log system of the exemplary embodiment;

FIG. 4 is a flowchart illustrating a process of the exemplary embodiment;

FIG. 5 is a flowchart illustrating another process of the exemplary embodiment;

FIG. 6 diagrammatically illustrates a process of the exemplary embodiment; and

FIG. 7A and FIG. 7B illustrate the screen of a terminal of the exemplary embodiment.

DETAILED DESCRIPTION

An exemplary embodiment of the present invention is described with reference to the drawings.

FIG. 1 illustrates a system configuration of a document management system of the exemplary embodiment. The document management system includes a terminal 10, a document processing apparatus 12, and a log system 14. The terminal 10, the document processing apparatus 12, and the log system 14 are connected to each other via a communication network for data communication. The communication network may be a local area network and/or the Internet, and may be an exclusive network or a public network. The communication network may be a wired network and/or a wireless network.

The terminal 10 may be a personal computer (PC), a tablet terminal, or a smart phone, and may be a device that a user uses to search a document.

The document processing apparatus 12 is a multi-function apparatus, an image forming apparatus, or a PC, which processes a document. The document processing apparatus 12 supplies a processed document to the log system 14 via the communication network. For example, the document processing apparatus 12 as a multi-function apparatus obtains document data by scanning a document, and then supplies the document data to the log system 14 via the communication network.

The log system 14, functioning as a document management apparatus, receives and stores document data processed by the document processing apparatus 12. If confidential information is included in the received document data, the log system 14 sorts the document data into the confidential information and non-confidential information while at the same time generating and storing a confidential information index for the confidential information and a non-confidential information index for the non-confidential information. The log system 14 stores the received document data after performing a predetermined concealment operation on the confidential information. Upon receiving a search request from the terminal 10, the log system 14 searches a document by switching between the confidential information index and the non-confidential information index, and returns a search result to the terminal 10. If the search is hit in a portion of the confidential information that has undergone the concealment operation, the log system 14 returns, together with the search result, a location of the portion, where the search is hit, of the confidential information having undergone the concealment operation.

In accordance with the exemplary embodiment, the log system 14 stores the document data in which the confidential information is concealed. A user having no special right is unable to search using the confidential information index, and thus confidentiality is maintained. Even a user having no special right is able to search using the non-confidential information index. A user having a special right is able to search using the confidential information index. Searchability is thus maintained. In accordance with the exemplary embodiment, a hit location concerning the confidential information portion that has undergone the concealment operation is also indicated in addition to returning the search result indicating that the search is hit. A user who is not entitled to recognize the confidential information may still be able to recognize and trace the location of the confidential information within the entire document, and traceability is thus maintained. The word “confidentiality” means that a user who has no right to access the confidential information is not allowed to make reference to the confidential information. The word “searchability” means that even if a user who has no right to access the confidential information is still able to search information and recognize contents of the information other than the confidential information. The word “traceability” refers to a capability to identify who has leaked a document outside if the document has actually been leaked out. More specifically, the word “traceability” is a capability to determine whether or not a document stored in the log system 14 is identical to a leaked document.

FIG. 2 is a functional block diagram illustrating the log system 14.

The log system 14 includes, as functional blocks, a document receiving unit 14 a, a non-confidential information character string identifying unit 14 b, a confidential information index storage unit 14 c, a non-confidential information index storage unit 14 d, a document storage unit 14 e, a search target index controller 14 f, a confidential information character string identifying unit 14 g, a confidential information index generating unit 14 h, a non-confidential information index generating unit 14 i, a confidential information character string concealing unit 14 j, an access right management unit 14 k, a search processor 14 m, a character string location storage unit 14 n, and a table storage unit 14 p.

The document receiving unit 14 a receives the document data supplied from the document processing apparatus 12. The document data may include not only character data but also image data. The image data included in the document data may include, in addition to a picture pattern image such as a photograph and a graph, a line image and a character image.

The confidential information character string identifying unit 14 g identifies a character string of the confidential information included in the document data by a character string search according to a regular expression (a character string pattern composed of normal characters and special characters) or a simple character string search. The regular expression for identifying the confidential information may include a form, such as a credit card number, an address, or a personal number, and the regular expression and the character string corresponding to the confidential information are set in advance and registered by an administrator in the log system 14. If a process target is text data, the confidential information is searched for in the text data, and if the process target is image data, the image data is converted into text data through optical character recognition (OCR), and the confidential information is then searched for.

The non-confidential information character string identifying unit 14 b identifies, as the non-confidential information character string, a character string other than a character string, identified as the confidential information by the confidential information character string identifying unit 14 g, out of the received document data.

The confidential information index generating unit 14 h generates, as a first search index, a confidential information index for the character string identified by the confidential information character string identifying unit 14 g. The confidential information index includes a document data identifier that identifies document data (currently under process) including the character string identified as the confidential information character string, and location information that identifies a location of the confidential information character string in the document data.

The confidential information index storage unit 14 c, functioning as a third memory, stores a confidential information index generated by the confidential information index generating unit 14 h. A user having a special right to access the confidential information is entitled to access the confidential information index storage unit 14 c.

The non-confidential information index generating unit 14 i generates the non-confidential information index as a second search index for the character string identified by the non-confidential information character string identifying unit 14 b. The non-confidential information index includes a document data identifier identifying the document data (currently under process) including the character string identified as the non-confidential information character string and location information identifying a location of a non-confidential information character string in the document data.

The non-confidential information index storage unit 14 d, functioning as a fourth memory, stores the non-confidential information index generated by the non-confidential information index generating unit 14 i. The non-confidential information index storage unit 14 d is accessible through an access right different from the access right through which the confidential information index storage unit 14 c is accessible. More specifically, even a user who has no right to access the confidential information may access the non-confidential information.

The confidential information character string concealing unit 14 j conceals the character string identified by the confidential information character string identifying unit 14 g by converting the character string into a character string in an unviewable state which a user is unable to view. Specifically, the unviewable states include deletion and blackout, but are not limited to these states. The document data with the confidential information concealed is data that does not include the confidential information. By processing the document data into “concealed document data”, the confidential information remains unviewable even if the document data stored in the log system 14 leaks out. Confidentiality of the document data is thus maintained.

The document storage unit 14 e, functioning as a first memory, stores the document data with the confidential information thereof concealed by the confidential information character string concealing unit 14 j.

The access right management unit 14 k manages the access right of each user. Specifically, the access right management unit 14 k references a table that defines the access right of each user in advance, and determines the access right of the user. In accordance with the exemplary embodiment, the access right management unit 14 k determines the access right of the user, in particular, determines whether the user has the access right to the confidential information.

The search target index controller 14 f switches from one search target index to another depending on the user's access right. Specifically, the search target index controller 14 f allows an ordinary user to access the non-confidential information index storage unit 14 d with only the non-confidential information index serving as a search target. The search target index controller 14 f allows a user having a special right for accessing the confidential information to access the non-confidential information index storage unit 14 d and the confidential information index storage unit 14 c with the confidential information index in addition to the non-confidential information index serving as search targets.

More specifically, users with ordinary right: non-confidential information index, and users with special right: non-confidential information index+confidential information index. The search index is switchably used depending on the access right of each user.

The search processor 14 m, functioning as a searching unit, performs search in accordance with a search condition specified by the user, and returns a search result to the user, namely, the terminal 10. If the search condition is satisfied (is hit), the document data stored in the document storage unit 14 e as the search result, namely, the document data having the confidential information concealed therewithin is returned to the terminal 10.

The character string location storage unit 14 n, functioning as a replacing unit, stores location information of the confidential information character string.

Specifically, the character string location storage unit 14 n generates a dummy character string uniquely associated with the confidential information, and causes the dummy character string to replace the confidential information, thereby embedding the dummy character string into the location where the confidential information has been. The character string location storage unit 14 n generates a table that defines a relationship between the confidential information and the dummy character string associated therewith, and stores the table in the table storage unit 14 p serving as a second memory. The dummy character string includes symbols (including a control code) not used as a search character string. When the confidential information is specified as a search condition in a search request from the terminal 10, the character string location storage unit 14 n identifies the dummy character string by referencing the table stored in the table storage unit 14 p, and identifies the location of the confidential information by searching the document data for the dummy character string instead of the confidential information included in the search condition. Specifically, the dummy character string replaces the location information that indicates the location of the confidential information. In this case, the confidential information index is used.

In accordance with the exemplary embodiment, the dummy character string replaces the confidential information, and the dummy character string is used as the location information indicating the location of the confidential information. The character string location storage unit 14 n may simply store the location information of the confidential information character string without replacing the confidential information with the dummy character string. If the terminal 10 specifies the confidential information as the search condition in the search request thereof, the character string location storage unit 14 n identifies the location of the confidential information included in the search condition using the location information. In such a case, the table that defines the relationship between the confidential information and the dummy character string associated therewith is not used.

FIG. 3 is a configuration block diagram illustrating the log system 14.

The log system 14, functioning as a document management server or a document searching server, has a configuration as a server computer. Specifically, the log system 14 includes one or more central processing units (CPUs), a read only memory (ROM), a random access memory (RAM), an input and output interface (I/F), a communication I/F, and a memory. The communication I/F is connected to a communication network, exchanges data with each of the terminal 10 and the document processing apparatus 12. The memory is a hard disk drive (HDD), or a solid-state drive (SSD).

One or more CPUs read and execute processing programs stored in the ROM or memory, thereby implementing the functional blocks of FIG. 2. Upon receiving the document data from the document processing apparatus 12 via the communication I/F, the CPU identifies the confidential information character string from the document data, while also identifying the non-confidential information character string. The CPU generates a confidential information index for the confidential information character string and a non-confidential information index for the non-confidential information character string. The CPU stores the generated confidential information index in a confidential information index storage region of the memory, and the generated non-confidential information index in a non-confidential information index storage region of the memory.

One or more CPUs perform a concealment operation by blacking out the confidential information character string identified in the document data and then store the concealment processed document data in the memory.

The one or more CPUs replace the confidential information character string with the dummy character string, generates the table that defines the relationship between the confidential information character string and the dummy character string, and stores the table in the memory.

When a user logs in on the log system 14 using the terminal 10, the CPU authenticates the user using an identification and a password of the user, and verifies the access right of the user who has logged in (login user). The access right of each user is specified in the table stored in the memory. By referencing the table, the CPU determines whether the logged-in user has the access right to the confidential information. If the logged-in user has no access right to the confidential information, the CPU performs search using only the non-confidential information index as a search target index. If the logged-in user has a special right to access the confidential information, the CPU performs search using the non-confidential information index and the confidential information index as the search target indexes. The CPU returns the search result to the terminal 10. Given the same search condition, the search result may be different depending on whether the user has the special right or not.

The one or more CPUs function as each of the confidential information character string identifying unit 14 g, the non-confidential information character string identifying unit 14 b, the confidential information index generating unit 14 h, the non-confidential information index generating unit 14 i, the confidential information character string concealing unit 14 j, the access right management unit 14 k, the search target index controller 14 f, the search processor 14 m, and the character string location storage unit 14 n. The communication I/F functions as the document receiving unit 14 a. The memory functions as each of the confidential information index storage unit 14 c, the non-confidential information index storage unit 14 d, the document storage unit 14 e, and the table storage unit 14 p.

Some of the functional blocks of FIG. 2 may be implemented using hardware instead of using software that executes a program. The hardware may be implemented using a circuit, such as an application specific integrated circuit (ASIC) or a field programmable gate array (FPGA).

FIG. 4 is a flowchart illustrating a process of the log system 14 of the exemplary embodiment. The process includes an index generation operation, a concealment operation, and a storage operation.

Upon receiving the document data from the document processing apparatus 12 via the communication I/F (S101), the CPU in the log system 14 identifies all the confidential information character strings in the document data (S102). For example, if a credit card number is included in the document data, that credit card number is identified as a confidential information character string.

The CPU then determines whether there is any unprocessed confidential information character string (S103). The “unprocessed” here means that an index is not produced yet. If there is an unprocessed confidential information character string (yes from S103), the CPU selects one confidential information character string as a process target (S104), and generates a confidential information index from the confidential information character string (S105). The index is expressed in a form of list of appearing locations of words, characters, and character strings included in the document. The index may be an inverted index that expresses a document where each of the words, characters, and character strings appears, and expresses the location of each of the words, characters, and character strings in the document. In analysis of the words, characters, and character strings in the document, morphological analysis or N-gram may be used. After an index is generated for the confidential information, the confidential information index is stored in the memory, namely the confidential information index storage unit 14 c (S106).

The CPU performs the concealment operation of the selected confidential information character string (S107). The concealment operation may black out the character string, for example. The confidential information character string having undergone the concealment operation is marked with a flag indicating completion of concealment (S108).

The CPU generates the dummy character string associated with the selected confidential information character string, embeds the dummy character string at a concealment information location, and adds to the table the relationship between the confidential information and the dummy character string (S109). Operations in S104 through S109 are performed on each of all the confidential information character strings in the document data. If the confidential information is not replaced with the dummy character string, these operations are not performed.

The CPU performs the index generation operation, the concealment operation, and table addition operation on each of all the confidential information character strings in the document data (no branch from S103). The CPU then identifies a non-confidential information character string (S110), and generates a non-confidential information index from the non-confidential information character string (S111). In a similar manner as in the confidential information character string, the inverted index that expresses a document in which each of the words, characters, and character strings appears, and the location thereof in the document may be used. In analysis of the words, characters, and character strings in the document, morphological analysis or N-gram may be used. After an index is generated for the non-confidential information, the non-confidential information index is stored in the memory, namely the non-confidential information index storage unit 14 d (S112).

The CPU generates and stores the confidential information index and the non-confidential information index, and performs the concealment operation on the confidential information character string. The CPU then stores the document data having undergone the concealment operation in the memory, namely, in the document storage unit 14 e (S113).

FIG. 5 is a flowchart illustrating another process performed by the log system 14 of the exemplary embodiment.

The user accesses the log system 14 using the terminal 10, and logs in using an ID and a password (S201). The CPU adds the non-confidential information index as a search target index (S202).

The CPU then verifies the access right of the logged-in user by referencing the table that defines the right of each user in advance, and determines whether the user has the right to access the confidential information (S203).

If the user has no right to access the confidential information (no branch from S203), the search target index remains unchanged from the index added in S202. On the other hand, if the user has the right to access the confidential information (yes from S203), the CPU adds the confidential information index as a search target index (S204).

After switching from one search target index to another in response to the access right, the CPU performs search using the search target index (S205), and returns the search result to the terminal 10 (S206). If the confidential information character string is specified as a search condition, the CPU identifies the dummy character string by referencing the table stored in the table storage unit 14 p, and then performs search based on the premise that the dummy character string is specified as the search condition. In this sense, the table may be considered to be a table that converts the search condition from the confidential information to the dummy character string. If the search is performed using the dummy character string and is hit, the CPU returns the search result together with the hit location. Since the confidential information is blacked out in the concealment operation, the hit location indicates the location of the concealed portion. If the confidential information is not replaced with the dummy character string, the location information of the confidential information character string included in the search condition is returned to the terminal 10.

FIG. 6 diagrammatically illustrates a process of the exemplary embodiment.

A document 100 is received from the document processing apparatus 12, and includes confidential information. The document 100 has not undergone the concealment operation.

The log system 14 identifies a confidential information character string in the document 100, generates a confidential information index for the confidential information character string, and stores the confidential information index in the confidential information index storage unit 14 c. The log system 14 generates a non-confidential information index for a non-confidential information character string other than the confidential information character string, and stores the non-confidential information index in the non-confidential information index storage unit 14 d. The log system 14 generates a document 102 by performing the concealment operation on the confidential information character string (blacks out the confidential information character string as illustrated in FIG. 6). The document 102 is stored as a document 104 in the document storage unit 14 e.

The user performs search on the document 104 stored in the document storage unit 14 e. A user 200 having a special right searches the document 104 using the confidential information index stored in the confidential information index storage unit 14 c, and the non-confidential information index stored in the non-confidential information index storage unit 14 d. If a search key word includes the confidential information index, the confidential information index is hit in the search, and the hit results are returned. The hit results are displayed on the screen of the terminal 10. The user 200 may thus recognize the document 104 (but the confidential information character string is blacked out and remains unrecognizable). On the other hand, a user 202 having no special access right searches the document 104 using only the non-confidential information index stored in the non-confidential information index storage unit 14 d. Even if a search key word includes the confidential information character string, the confidential information character string is not hit in the search. The user 202 is unable to recognize the presence of the document 104. Referring to FIG. 6, an arrow-headed broken line and an X symbol indicate that the confidential information index storage unit 14 c remains inaccessible.

In accordance with the exemplary embodiment, the access right is not assigned on a per index basis, and search is performed by switching search target indexes on a per access right basis. Confidentiality of a document to be managed is maintained, and searchability is assured without a substantial delay in processing performance.

FIG. 7A and FIG. 7B illustrate display examples displayed on a screen 11 of the terminal 10 that has received the search result from the log system 14.

The document 104 that is hit in the search is displayed on the screen 11. As previously described, the document 104 is a document that has undergone the concealment operation, namely, the confidential information is concealed by blackout 300. Together with the document 104, the location that the search condition matches is displayed in relation to the blackout 300. Referring to FIG. 7A, the matched location is displayed as information 302 in a particular shape, specifically, a rectangular shape. The dummy character string is present in the matched location.

The information 302 indicating the matched location may be represented by any shape. As illustrated in FIG. 7B, the matched location in the blackout 300 may be represented by a particular colored outline, for example, a red outline.

The CPU not only displays the document 104 having undergone the concealment operation as the search result, but reports the location that is in the portion having undergone the concealment operation and satisfies the search condition. Traceability is thus assured. There is a possibility that the document 100 including the confidential information leaks. If the location of the confidential information included in a presumably leaked document matches the location of the confidential information in the document 104, the document 100 is definitely determined to have leaked.

The exemplary embodiment of the present invention has been described. The present invention is not limited to the exemplary embodiment. The exemplary embodiment may be modified in a variety of forms. Modifications are described below.

First Modification

In accordance with the exemplary embodiment, the confidential information index generating unit 14 h generates the confidential information index for the confidential information character string identified by the confidential information character string identifying unit 14 g. Alternatively, the confidential information index generating unit 14 h may generate the confidential information index by including the confidential information character string and character strings prior to and/or subsequent to the confidential information character string. For example, in the case of character strings “character string A <confidential information character string> character string B”, a confidential information index may be generated using character string A <confidential information character string> as a combination of the confidential information character string and the character string A prior to the confidential information character string. Also, a confidential information index may be generated using <confidential information character string> character string B as a combination of the confidential information character string and the character string B subsequent to the confidential information character string. Alternatively, a confidential information index may be generated using character string A <confidential information character string> character string B as a combination of the confidential information character string and the character strings A and B respectively prior to and subsequent to the confidential information character string.

In this way, search is performed using a search key word including a mixture of the non-confidential information and the confidential information.

The administrator may set and register in the log system 14 in advance as to how many strings in the non-confidential character strings prior to and subsequent to the confidential information character string are to be included.

Second Modification

In accordance with the exemplary embodiment, the character strings of the document data are sorted into the confidential information character strings and the non-confidential information character strings. The confidential information character strings may be sorted according to multiple levels depending on the degree of confidentiality, and an index may be generated depending on the level of confidentiality. For example, the confidential information character strings may be sorted into the confidential information character strings at a level 1 and the confidential information character strings at a level 2 (the level 2 has a higher degree of confidentiality than the level 1). A confidential information index at the level 1 is generated for the confidential information character string at the level 1 and stored in the memory, and a confidential information index at the level 2 is generated for the confidential information character string at the level 2 and stored in the memory. Search is performed depending on the access right of each user. For example, search may be performed using the non-confidential information index for a user having no special right. Search may be performed by adding the confidential information index at the level 1 for a user having a special right at the level 1, and search may be performed by adding the confidential information index at the level 2 for a user having a special right at the level 2.

Third Modification

In accordance with the exemplary embodiment, the first memory, the second memory, the third memory, and the fourth memory are included in the same memory. These memories may be separate memory media. For example, a storage medium forming the first memory may be different from a storage medium forming the second through fourth memories.

In accordance with the exemplary embodiment, the confidential information index storage unit 14 c is differentiated from the non-confidential information index storage unit 14 d as illustrated in FIG. 2. The confidential information index storage unit 14 c and the non-confidential information index storage unit 14 d are not necessarily different units. The confidential information index and the non-confidential information index may be simply managed as different search indexes. For example, the confidential information index may be stored with a flag indicating the confidential information index.

Fourth Modification

In accordance with the exemplary embodiment, the log system 14 identifies the confidential information included in the received document data. Alternatively, a unit other than the log system 14 may identify the confidential information and transfer the identified confidential information to the log system 14.

In the configuration of FIG. 1, the document processing apparatus 12 transmits the document data to the log system 14. Alternatively, the document processing apparatus 12 may identify the confidential information in the document data, and may transmit the identified confidential information together with the document data to the log system 14.

Fifth Embodiment

In accordance with the exemplary embodiment, the confidential information index is generated from the confidential information, and the non-confidential information index is generated from the non-confidential information. Alternatively, the first search index may be generated from the whole document data including the confidential information and the second search index may be generated from the non-confidential information excluding the confidential information. In such a case, the search using the first search index is performed for a user having a special right, and the search using the second search index is performed for a user having no special right.

Sixth Modification

In accordance with the exemplary embodiment, the confidential information character string is replaced with the dummy character string after the concealment operation is performed on the confidential information character string as illustrated in FIG. 4. Alternatively, the concealment operation may be performed after the confidential information character string is replaced with the dummy character string. The operation of replacing the confidential information character string with the dummy character string may be identical to the concealment operation if the original confidential information becomes unrecognizable.

Seventh Modification

In accordance with the exemplary embodiment, the first search index is generated based on the confidential information, the second search index is generated based on the non-confidential information, and the search is performed with the search index switched depending on the user's right. The search index may be generated from the whole document data as in the related art, and the confidential information character string may be replaced with the dummy character string, and the concealment operation may be performed on the dummy character string. The document data may then be stored in the document storage unit 14 e. Regardless of searchability, traceability is maintained with confidentiality maintained.

Eighth Modification

In accordance with the exemplary embodiment, the location information that the search condition matches in the search for the user having the special right is also returned as the search result to the terminal 10. A determination as to whether to return the location information that the search condition matches may be made depending on the level of the special right. Alternatively, a determination as to whether to return the location information that the search condition matches may be made in response to a request from the user having the special right.

The foregoing description of the exemplary embodiment of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiment was chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the special use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents. 

What is claimed is:
 1. A document management apparatus comprising: a first memory that stores document data in which confidential information is concealed; a second memory that stores a first search index that is generated for the confidential information included in the document data; a third memory that stores a second search index that is generated for non-confidential information other than the confidential information; a display controller that, in searching the document data according to an input search condition, displays a location where the confidential information included in the input search condition is located in a concealment portion in the document data when the document data stored in the first memory and including the confidential information included in the input search condition is displayed as a search result, wherein the document data is searched by switching between the first search index and the second search index depending on a right assigned to a user; and a searching unit that searches the document data using the first search index and the second search index for a user having a special right, and searches the document data using the second search index for a user having no special right.
 2. The document management apparatus according to claim 1, wherein the search result comprises, in the concealment portion, information of a location that satisfies the search condition.
 3. The document management apparatus according to claim 1, wherein the first search index is generated from a character string of the confidential information.
 4. The document management apparatus according to claim 1, wherein the first search index is generated from a linked character string including a character string of the confidential information, and at least one of character strings of non-confidential information prior to and subsequent to the character string of the confidential information.
 5. The document management apparatus according to claim 1, wherein the first search index is generated from a character string of the document data including the confidential information.
 6. A document management system comprising: a document processing apparatus; a document management apparatus that receives document data from the document processing apparatus, the document management apparatus including a first memory that stores document data in which confidential information is concealed, a second memory that stores a first search index that is generated for the confidential information included in the document data, a third memory that stores a second search index that is generated for non-confidential information other than the confidential information, and a display controller that, in searching the document data according to an input search condition, displays a location where the confidential information included in the input search condition is located in a concealment portion in the document data when the document data stored in the memory and including the confidential information included in the input search condition is displayed as a search result, wherein the document data is searched by switching between the first search index and the second search index depending on a right assigned to a user; and a searching unit that searches the document data using the first search index and the second search index for a user having a special right, and searches the document data using the second search index for a user having no special right a terminal that transmits the search condition to the document management apparatus and receives the search result from the document management apparatus.
 7. A non-transitory computer readable medium storing a program causing a computer to execute a process for managing document data, the process comprising: concealing confidential information of the document data; storing, on a first memory, the document data having the confidential data concealed therewithin; storing, on a second memory, a first search index that is generated for the confidential information included in the document data; storing, on a third memory, a second search index that is generated for non-confidential information other than the confidential information; in searching the document data according to an input search condition, displaying a location where the confidential information included in the input search condition is located in a concealment portion in the document data when the document data stored in the memory and including the confidential information included in the input search condition is displayed as a search result, wherein the document data is searched by switching between the first search index and the second search index depending on a right assigned to a user; and searching the document data using the first search index and the second search index for a user having a special right, and searches the document data using the second search index for a user having no special right. 